Rotary tool with balancing rings

ABSTRACT

A rotary tool, in particular a high-speed milling or boring tool, has at least two balancing rings (17, 18) with a variable mass around their circumference mounted on the tool holder or tool body (1). Two concentric balancing rings (17, 18) whose position in relation to the axis of rotation (6) of the tool (1) may be adjusted are releasable mounted in the tool holder or in the tool body (1) and are supported in the radial direction (14) in the tool holder or tool body (1). A short rotary tool (1) is thus obtained with a simple support of the balancing rings (17, 18) in the radial direction.

The present invention relates to a rotary tool, in particular ahigh-speed milling or boring tool, in accordance with the preamble tothe main claim.

Rotary tools with balancing rings of this type are disclosed, forexample, in U.S. Pat. No. 5,263,995 or in U.S. Pat. No. 5,074,723. Thedisadvantage of such rotary tools comprising tools as well as toolholders, which operate at very high speeds, for example in the order ofup to 20,000 revolutions per minute, is the problem of fine balancing ofthe tools and the tool holders. In accordance with the prior art, e.g.as represented through the two aforementioned U.S. patents, twobalancing rings are disposed to this end on the circumference of thetool or the tool holder at an axial distance from each other. Thesebalancing rings for the purpose of fine balancing are slidable withtheir inner circumference on the outer circumference of the rotary toolor the rotary tool holder in the circumferential direction and can befixed in different rotating positions relative to the tool body or thetool holder body. In particular, this relative slidability of thebalancing rings in relation to the tool body or the tool holder body iscontinuously variable.

The balancing rings for fine balancing are provided with a variable massaround their circumference. This is most easily attained by boringthrough the balancing rings in certain circumferential areas. Forexample, these could be bore holes running parallel to the axis ofrotation of the tool or the tool holder, whereby a reduction in mass canbe attained in the affected circumferential area of the balancing ringin question.

The balancing of kinetic energy, i.e. the fine balancing, is thenachieved through the fact that at least one of the balancing rings,preferably however both rings are moved to a rotating position inrelation to the tool or the tool holder and are fixed in this positionat which the balancing of kinetic energy is at its desired fineness.

The constructive design of the carrier body--whether this is the toolbody or the tool holder body--in accordance with the prior art has thedisadvantage that, during operation, the balancing rings are subject toconsiderable centrifugal forces as a result of the high speeds and arethereby weakened in their cross-section and could burst in the area ofthe bore holes in the balancing rings as well as in the area of theclamping elements designed for fixing the balancing rings. A furtherdisadvantage of the known embodiments is the fact that the balancingrings lying adjacent to each other in the axial direction of the tool orthe tool holder require a certain face-to-face length, which leads to anincrease in the overall length of the tool body or the tool holder bodyin the axial direction.

The object of the present invention is therefore to further develop arotary tool, in particular a high-speed cutting or boring tool, of thetype mentioned at the beginning to such an extent that a shorter overalllength of the entire system formed by the tool holder as well as thetool itself can be attained through a space-saving arrangement of thebalancing rings. Furthermore, the present invention aims to support thebalancing rings at least partially on their outer circumference such asto reduce to a large extent, if not, completely rule out the risk ofdamaging the balancing rings and thereby also the tool through the highcentrifugal forces occurring while the tool is in operation.

This object is attained through the rotary tool in accordance with theinvention which is embodied according to the characteristic features ofthe main claim. The fact that two balancing rings are concentric to eachother and thereby are normally disposed on a common level to the axis ofrotation of the tool or the tool holder results in a short overalldesign of the entire system formed by the tool and the tool holder.Since the balancing rings are disposed within each other, they cansupport each other in a radial direction. The invention also providesfor the balancing rings themselves to be supported in a radial directionthrough the tool holder body or the tool body, so that the highcentrifugal forces occurring during operation that are exerted on thebalancing rings are fed via the outer circumference of the balancingrings into the material of the tool holder or the tool body and absorbedthere. This radial support of the balancing rings thereby eliminates orat least reduces to the maximum extent the risk of the balancing ringsbreaking in areas with reduced thickness or in those areas having boreholes to decrease the mass of the balancing rings and/or to fix saidrings along the circumference.

To attain a particularly simple and secure arrangement of the balancingrings in a desired position, the rotary tool in accordance with theinvention is further developed as is secured in claim 2. Suchconcentric, circular grooves can easily be embodied in corresponding endareas or flange-like sections of the tool body or of the tool holderwith the corresponding fitting for the insertion of at least onebalancing ring. The embodiment of circular grooves, concentric to theaxis of rotation, for the insertion of the balancing rings results inthe balancing rings being supported around their entire outercircumference and thereby the centrifugal forces being correspondinglyabsorbed in the material of the tool holder or the tool body. If thearea of the end face or the flange-like area for insertion of thebalancing rings is made sufficiently large, a corresponding circulargroove can be made for each of the balancing rings to be used (at leasttwo), with one balancing ring being disposed within each such groove.However, in case of tight space conditions and so as to easily fix thedesired position of the balancing rings, a single circular groove forinsertion of both balancing rings can be sufficient in accordance withthe invention. In accordance with a particularly preferred embodiment,the circular groove for insertion of the balancing rings is dimensionedas indicated in claim 3.

As already indicated, care must be taken to correctly fix the balancingrings in relation to the tool holder or to the tool body. With a numberof insertion apertures corresponding to the balancing rings beingprovided, specifically grooves for the balancing rings, each balancingring must be designed with a suitable fixing or clamping device. In thecase that two balancing rings are inserted into the same groove in thetool holder or in the tool body, the balancing rings can be disposedsuch that only one of the two balancing rings need be designed with sucha fixing or clamping device.

To fix the balancing rings in a particularly simple and effectivemanner, the design is made in accordance with a preferred embodiment ofthe invention as secured in claim 5. Such clamping elements which areadjustable in the radial direction result in a splitting of theassociated balancing ring in the circular groove in the set rotatingposition against the body of the tool holder or of the tool itself,wherein the clamping elements can be radially adjusted through acorrespondingly adjustable clamping member. In accordance with aparticularly preferred embodiment, the clamping device is designed asshown in claim 6. Such splitting spheres can be inserted into simplebore holes of the corresponding balancing ring, wherein the clampingelement formed by the splitting sphere slides radially in acorresponding manner in the direction normally on the level of thebalancing ring as a result of screwing in a screw with a slope, forexample a countersunk flat screw. This results, first, in the balancingring designed with the clamping element being fixed to a side wall ofthe groove for insertion of the balancing ring, and secondly, in theother clamping element taking effect against the outer circumference ofthe adjacent balancing ring. In the same way, the other balancing ringwhich does not have its own clamping device is fixed at the same timeagainst the tool holder or the tool body.

The preferred embodiment for even spreading of the forces for fixing thebalancing ring is secured in claim 7.

Scales are designed, as indicated in claim 8, in order to provide for asuitably easy repeatability of the relative positioning of the balancingrings in relation to each other and in relation to the tool holder or tothe tool body.

A particularly space-saving embodiment of a rotary tool in accordancewith the invention while keeping the overall length as short as possibleis produced by using a milling cutter, as described in more detail inclaim 9. Since the milling cutter body must also have a sufficient axialextension in each case for insertion and fixing of the cutting edges andthereby has a corresponding material cross-section, at least one groovefor insertion of the balancing rings can be easily designed inaccordance with the invention on the end face opposite the cuttingdisks, such that the tool is not any longer in accordance with theinvention than a corresponding tool designed without balancing rings.

The invention is described below in more detail using the exemplaryembodiment shown in the accompanying drawing, in which the rotary toolin accordance with the invention is formed by a milling cutter. Thisshows:

FIG. 1 a side view--partially in cross-section--of a rotary tool inaccordance with the invention with inserted balancing rings,

FIG. 2 a top view of the rear side of the rotary tool from FIG. 1 in thedirection of arrow II, and

FIG. 3 a magnified sectional view of area III from FIG. 1.

The milling cutter body referenced in its entirety as 1, whichrepresents the rotary tool, has a steep taper 2 on its rear side forfixing a machine tool to the spindle and a flange-like cutter supporter3 on its front side. The exemplary embodiment shown is a surface millingcutter having cutting bodies 4 disposed on the front end face offlange-like cutter supporter 3.

As can be seen from FIG. 1, an end face 5 of cutting supporter 3, saidend face being opposite to cutting bodies 4, is disposed on a level thatis at right angles to axis of rotation 6 of the milling cutter. It isimportant that there is a step-like intermediate area between an outercircumference 7 of flange-like cutter supporter 3 and a shaftcircumference 8 of a milling cutter area adjoining backward-facing endface 5 on the rear side. A ring groove 10 being open to the rear side,i.e. to the side opposite cutters 4, and being concentric to axis ofrotation 6 in end face 5 is embodied in this stepped area 9.

The cross-sectional form of said ring groove 10 is particularly clearfrom FIG. 3. This has a groove base 11, an inner side wall 12 and anouter side wall 13. Ring groove 10 basically has a rectangularcross-section, wherein the effective width 15 of ring groove 10 in aradial direction 14 of rotary tool 1 is approximately twice the size ofa groove depth 16.

Within ring groove 10, an outer balancing ring 17 and an inner balancingring 18 are disposed concentric to each other, i.e. to axis of rotation6. Both balancing rings 17, 18 are designed in a circumferentialarea--shown at the top of FIG. 2--with bore holes 19 or 20 reducingtheir mass. Bore holes 19, 20 are positioned in an arc of a circleconcentric to axis of rotation 6 at equal distances from each other, andtheir boring axes basically run parallel to axis of rotation 6 of rotarytool 1.

The two balancing rings 17, 18 bear a scaling division 21 or 22 in theborder area to each other on their outside surface facing the rear sideof rotary tool 1. Both scaling divisions 21, 22 correspond to each otherand thereby provide for a particularly precise positioning while alsoallowing each rotating position to be repeated and documented. Ifnecessary, end faces 5 can also have a scaling in the area of groove 10.

The two balancing rings 17, 18 are sealed in an interlocking or slidingmanner to side walls 12, 13 of ring groove 10. In the embodiment shown,balancing rings 17 and 18 can be fixed with just one fixing or clampingdevice on one balancing ring, because balancing rings 17 and 18 aredisposed beside each other in the same recess or ring groove 10. Thefixing device connected to the outer balancing ring comprises acountersunk flat screw 25 that can be screwed into the outer balancingring 17 with its shank 26. The screw axis 27 runs parallel to axis ofrotation 6 of the body. While being screwed in, a countersunk head 28 ofscrew 25 with its cone-envelope-shaped circumferential surface spreadsapart the clamping elements formed by splitting spheres 29, 30 in radialdirection 14 of rotary tool 1. The inner splitting sphere 29 is herebypressed against inner balancing ring 18, and outer splitting sphere 30is pressed against outer side wall 13 of the groove. This pressingeffect not only securely fixes outer balancing ring 17 at thecircumference, but also securely fixes inner balancing ring 18 withinring groove 10, or against rotary body 1.

The two balancing rings 17, 18 can be adjusted in circumferentialdirection 23 by simply releasing fixing screw 25. As can be seen in FIG.2, two fixing screws or fixing devices 25 are disposed in areas of outerbalancing ring 17 that are diametrically opposite each other in order toensure a simple and symmetrical fixing of balancing rings 17 and 18.

By means of the shown embodiment with only one ring groove 10 and twobalancing rings 17, 18 being disposed therein and concentric to eachother, as already mentioned above, only one of the two balancing rings17 is given a clamping or fixing device, while, in the case ofseparately disposed balancing rings, both balancing rings disposedadjacent to each other require such a fixing device.

In accordance with the embodiment shown, outer balancing ring 17, whichis provided with the fixing device that weakens the ring cross-section,is directly supported around its entire circumference on outer side wall13 of ring groove 10 in a particularly effective manner against thecentrifugal forces exerted on it. Inner balancing ring 18 is also givensuch an effective support in the radial direction through itsarrangement on an inner ring wall 31 of outer balancing ring 17.

Instead of the direct arrangement of at least one ring groove 10 forinsertion of balancing rings 17 and 18 in the body of tool 1 itself, analternative embodiment--for example in connection with a high-speeddrill, in which case it is of course not possible to fix balancing ringson the tool formed by the drill--can have the tool holder itself in astepped, flat area with at least one groove 10 for insertion ofconcentric balancing rings 17 and 18 within each other.

We claim:
 1. A rotary tool, in particular a high-speed milling or boringtool, having at least two balancing rings with a variable mass aroundtheir circumference mounted on the tool, the rotary tool having an axisof rotation,characterized by the fact that two concentric balancingrings, whose position in relation to each other and in relation to theaxis of rotation of the tool may be adjusted, are releasably mounted inthe tool and are supported radially adjacent one another.
 2. The rotarytool in accordance with claim 1,characterized by the fact that the tool(1) includes an end face substantially perpendicular to the axis ofrotation of the tool, the end face having at least one circular groovebeing concentric to the axis of rotation of the tool for insertion ofthe two balancing rings.
 3. The rotary tool in accordance with claim2,characterized by the fact that the width of the groove holding thebalancing rings in the radial direction of the tool is approximatelytwice the depth of the groove.
 4. The rotary tool in accordance withclaim 2characterized by the fact that the tool is formed as a millingcutter and that a groove for insertion of the balancing rings, is onthat end face of the milling cutter body that faces away from anycutting inserts.
 5. The rotary tool in accordance with claim1,characterized by the fact that at least one balancing ring includes atleast one clamping device.
 6. The rotary tool in accordance with claim5,characterized by the fact that two clamping devices are on the atleast one balancing ring and are diametrically opposite each other inrelation to the axis of rotation of the tool.
 7. The rotary tool inaccordance with claim 1,characterized by the fact that the balancingrings have a scale on at least one outward facing end face.
 8. Therotary tool in accordance with claim 1,characterized by the fact that aclamping force is provided to the balancing rings by a clamping memberthrough clamping elements which are adjustable in the radial directionwith respect to the tool axis as the clamping member is adjusted withinat least one of the balancing rings.
 9. The rotary tool in accordancewith claim 8,characterized by the fact that the clamping elements areformed of splitting spheres and that the clamping member is formed of ascrew having a tapered surface.
 10. A rotary tool having an axis ofrotation and comprising:at least two balancing rings with a variablemass around their circumference, each of the balancing rings beingadjustably positioned in relation to each other and in relation to theaxis of rotation, and each of the balancing rings being releasablymounted radially adjacent each other in the tool; and at least one ofthe balancing rings has a clamping force provided thereto by a clampingmember through radially adjustable clamping elements as the clampingmember is adjustably positioned in the respective balancing ring. 11.The rotary tool of claim 10 wherein the clamping elements are formed ofsplitting spheres and that the clamping member is formed of a screwhaving a tapered surface thereon.
 12. The rotary tool of claim 10wherein the at least one balancing ring includes two clamping memberswith radially adjustable clamping elements, where the clamping membersare diametrically opposed to each other in relation to the axis ofrotation.
 13. A rotary tool having an axis of rotation and comprising:atool body for receiving a machine tool, the tool body including anannular groove therein that is substantially radial to the axis ofrotation, and the groove including an innermost surface, an outermostsurface and a base surface; an innermost balancing ring adjustablypositioned along the innermost surface and in relation to the axis ofrotation; and an outermost balancing ring adjustably positioned alongthe outermost surface and in relation to the innermost balancing ringand in relation to the axis rotation, whereby the balancing rings areradially adjacent one another along the axis of rotation.
 14. The rotarytool of claim 13 wherein the balancing rings are radially stacked oneach other.
 15. The rotary tool of claim 13 wherein the tool bodyincludes an end face substantially perpendicular to the axis of rotationand including the annular groove therein.
 16. The rotary tool of claim13 wherein at least one of the balancing rings has a clamping forceprovided thereto by a clamping member through radially adjustableclamping elements as the a clamping member is adjustably positioned inthe respective balancing ring.
 17. The rotary tool of claim 16 whereinthe clamping elements are formed of splitting spheres.
 18. The rotarytool of claim 17 wherein the clamping member is formed of a screw havinga tapered surface thereon.
 19. The rotary tool of claim 18 wherein theat least one balancing ring includes two clamping devices that arediametrically opposed to each other in relation to the axis of rotation.